Nonalcoholic fatty liver disease (NAFLD) is estimated to affect 1/3 of the US adult population. In this high-fat environment, hepatic mitochondria and peroxisomes are thought to work in concert to prevent lipid accumulation;however, enhanced peroxisomal activity generates reactive oxygen species (ROS) and may have damaging effects on hepatocytes. Exercise is considered among the best treatments for NAFLD, but there is little molecular explanation for its benefits. We have developed a mitochondrial trifunctional protein (catalyzes last 3 steps in beta-oxidation) heterozygous mouse (MTPa) that develops NAFLD and insulin resistance due to impairment in mitochondrial fatty acid oxidation and accumulation of long chain fatty acid metabolites. The central hypothesis of this proposal is that daily exercise increases hepatic mitochondrial biogenesis in MTPa mice resulting in increased mitochondrial fatty acid oxidative capacity and reduced trafficking of fatty acids through peroxisomal pathways culminating in reduced hepatic-oxidative stress, -steatosis, and liver injury. We also postulate that this reduced hepatic oxidative stress will improve hepatic insulin signaling and whole body insulin sensitivity. MTP and MTP mice will either voluntarily exercise on running wheels or remain sedentary for 6 months. Measures of hepatic mitochondrial biogenesis and peroxisomal proliferation and fatty acid oxidative capacity will be assessed, along with hepatic lipid peroxidation and oxidative stress. MTP mice also will undergo hyperinsulinemic-euglycemic clamps to assess the influence of exercise on hepatic insulin signaling and whole-body insulin sensitivity. The long-term goal of this project is to explore mechanisms linked to reduced severity of hepatic steatosis with exercise training. PUBLIC HEALTH RELEVANCE: It also is estimated that more than 10 million Americans have disorders in mitochondrial fatty acid oxidation and 90 million US adults have NAFLD. Unfortunately, the effectiveness and biological mechanisms of current treatments are largely unknown. It is the focus of this project to identify potential mechanisms and therapeutic targets by which exercise can reduce the incidence of NAFLD by increasing hepatic mitochondrial function, reduce liver injury, and improve hepatic insulin sensitivity.